The invention relates to an oil pump with a pump plunger arranged in a pump casing and able to perform lifting movements by means of a drive for hand rail chain saw machines.
Valveless-controlled plunger pumps have been mainly used for the lubrication of the cutting chain in motor saws of the aforementioned type. The pumps are driven by a worm drive or a combined worm-toothed gear drive. As a particularly lightweight, compact construction is required for motor saws, this requirement also applies to the oil pump, although its function must not be impaired.
In connection with this requirement, the sealing of the pump plunger shaft is particularly difficult, because it is very short due to the compact construction and consequently sucks in air via the plunger shaft during the suction phase accompanied by increased suction resistance, either due to cold, i.e. viscous oil or due to contamination of the suction filter. This is prejudicial to the operation of the pump and the contact surface of the plunger and the drive in general becomes generally free from lubricant and is consequently exposed to increased wear.
In the case of the known oil pumps for motor saws, this problem is either unsolved or only partly solved. Known solutions are accurate cylinder fits or seals by O-rings or long plungers.
All these solutions have the disadvantage that they are not free from wear and do not ensure an adequate lubrication of the drive.